The first step in creating a section is to select the ducts to include. In drawing M1, go to
DM HVAC 
Sections and 3D Drafting Create Sections
The Duct Sections dialog box will appear as shown below.
Press New Section. The New Section dialog box will appear as shown below.
Type "A" for Section Name and press OK. You will be returned to the Duct Sections dialog box, which will now contain section A under Section Names as shown below.
Make certain section A is selected as shown above and press Add Ducts. Design Master HVAC will take you to the drawing and prompt you to select objects. Draw a crossing box around the ducts in Conference 102 as shown below.
When all the ducts in Conference 102 are included in the crossing box as shown above, specify the opposite corner of the crossing box and press ENTER. You will again be returned to the Duct Sections dialog box. Press Draw Cutline. Design Master HVAC will prompt you to select the first point for the section cutline. Select a point to the right of Conference 102 as shown below (the finished cutline is highlighted in yellow). You will then be prompted to select the second point. Click to indicate a second point that will create a cutline similar to the one shown and highlighted in yellow in the drawing below.
Finally, Design Master HVAC will prompt you to pick a point on the side to face (as shown above). Click on a point to the left of the cutline. You will be returned to the Duct Sections dialog box. Press Exit. Your drawing should now match the one shown below.
You now have defined your section. Next, you will insert the actual section on a drawing.